An unbelievable situation at a client.

2 people looking at the same spreadsheets from the same email on their computers saw different results. After some investigation it was discovered that the one had the Analysis Toolpack switched on and the other off.

In  most situations this would result in a number of error messages which would obviously identify that the Analysis Toolpack should be switched on. However, because the spreadsheet was built with many error checks built in (if a formula is #NA! do something), it actually just changed the results.

Therefor it is important to document your spreadsheet and where necessary specify that the Analysis Toolpack be switched on.